PVDF-based solid-state electrolyte, and preparation method and application thereof

Abstract

The application discloses a PVDF-based solid electrolyte and a preparation method and application thereof, and relates to the technical field of batteries, and specifically discloses a PVDF-based solid electrolyte, which comprises a PVDF polymer matrix, a lithium salt, an organic ionic plastic crystal material and residual solvent. The PVDF-based solid electrolyte provided by the application is applied to a lithium metal battery, can improve lithium ion migration capacity, reduce an ion migration energy barrier, and improve capacity retention rate and cycle stability of the battery.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, specifically relating to a PVDF-based solid electrolyte, its preparation method, and its application. Background Technology

[0002] Lithium metal anodes possess extremely high theoretical specific capacity and the lowest electrochemical potential, making them a promising anode material for high-energy-density batteries. However, lithium metal batteries still face challenges in practical applications, such as dendrite growth and poor safety. Traditional organic carbonate electrolytes are flammable, volatile, and prone to leakage, failing to meet the demands of high-safety lithium metal batteries. Polymer solid electrolytes, due to their high safety, flexibility, ease of processing, and good interfacial contact, are considered a crucial pathway to solving the safety and interfacial stability issues of lithium metal batteries. Among them, polyvinylidene fluoride (PVDF) and its derivatives have gradually become a research hotspot in the field of polymer solid electrolytes due to their non-flammability, wide electrochemical window, good mechanical properties, and film-forming processing performance.

[0003] PVDF-based solid electrolytes are typically prepared by solution casting of PVDF, lithium salts, and polar solvents. However, due to the semi-crystalline nature of PVDF polymers, its crystallinity at room temperature is usually higher than 50%, severely hindering lithium-ion migration along amorphous regions. Furthermore, PVDF readily forms micron-sized spherulites and mesophase separation structures during film formation, leading to... + The transport path is discontinuous, and long-range ion conduction is limited, especially under high-rate and low-temperature conditions, the performance degrades significantly.

[0004] Furthermore, because PVDF lacks strong coordination sites similar to those in the ether oxygen in PEO, its lithium salt dissociation and Li + Transport often depends on residual polar solvents and Li + The formed solvated complex and the dynamic interaction between the complex and the CF dipole on the PVDF segment; too little residual solvent will lead to a decrease in conductivity, but too much residual solvent will trigger side reactions on the lithium metal anode and high-voltage cathode sides, resulting in a decrease in interface stability.

[0005] Therefore, it is difficult to achieve high ionic conductivity, high lithium-ion transference number, high mechanical strength, and high interfacial stability simultaneously by relying solely on PVDF polar segments or residual solvents. It is desirable to provide a new PVDF-based solid electrolyte to meet application requirements. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a PVDF-based solid electrolyte, its preparation method, and its applications.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a PVDF-based solid electrolyte, comprising a PVDF polymer matrix, a lithium salt, an organic ion-particle-based crystallizing material, and a residual solvent.

[0009] Organic ion-particle-shaped crystals possess the characteristics of ordered ionic crystal arrangement and disordered molecular orientation, combining ionic conductivity, a wide electrochemical window, and plastic deformation capability. This invention introduces organic ion-particle-shaped crystals into a PVDF-based solid electrolyte, enabling the absorption of these crystals through ion-dipole interactions and the participation of anions in Li... + The coordination structure and local orientation disorder in the plastic phase enable anchoring to polar solvents and optimize Li + Migration path.

[0010] That is, the present invention introduces an organic ion-particle-modifying material into an electrolyte system composed of a PVDF polymer matrix, lithium salt, and residual polar solvent, which has the following advantages:

[0011] 1. By introducing organic ion-plasticized materials, the state of residual polar solvent can be effectively controlled. By anchoring the solvent, its free movement can be restricted, reducing the tendency of free solvent to initiate interfacial side reactions and improving the stability of lithium metal anode interface and high-voltage cathode interface.

[0012] 2. By introducing organic ionic plasticizing materials, which include anions (e.g., FSI) - Able to participate in Li + In the solvation structure, it is beneficial to form a stable SEI layer containing inorganic components such as LiF, which further improves the interface stability of lithium metal anode;

[0013] 3. An interaction exists between the organic ion-particle-modified crystal material and the CF dipoles on the PVDF segments, optimizing Li + Transmission behavior on PVDF segments;

[0014] 4. Improve the ionic conductivity of solid electrolytes and the battery's performance at room temperature and low temperature;

[0015] Therefore, the PVDF-based solid electrolyte provided by this invention, when applied to lithium metal batteries, can improve lithium-ion migration ability, reduce ion migration energy barrier, and improve battery capacity retention and cycle stability.

[0016] In some embodiments, the residual solvent includes any one or a combination of at least two of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, or dimethyl sulfoxide, preferably N,N-dimethylformamide.

[0017] In some embodiments, based on the total mass of the PVDF-based solid electrolyte as 100%, the mass percentage of the residual solvent is 5-25 wt%, for example 5 wt%, 6 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 15 wt%, 20 wt%, 25 wt%, or any of the above values, preferably 5-20 wt%, more preferably 8-12 wt%.

[0018] In some embodiments, the PVDF polymer matrix includes any one or a combination of at least two of PVDF, PVDF-HFP, P(VDF-TrFE), P(VDF-TrFE-CTFE), or blends or derivatives of PVDF with the above copolymers.

[0019] In some embodiments, the lithium salt includes any one or a combination of at least two of LiFSI, LiTFSI, LiDFOB, LiBOB, LiBF4, LiPF6, LiClO4, or LiNO3, with LiFSI being preferred.

[0020] In some embodiments, the cationic structure of the organic ion-plasticized crystal material includes 1-ethyl-1-methylpyrrolidone ion (Pyr 12 + ), 1,1-dimethylpyrrolidine ononium ion (Pyr 11 + ) or dimethyldiethylammonium ion (N 1122 + Any one or at least two of the following, including anions such as FSI. - TFSI - DFOB - BOB - BF4 - or PF6 - Any one or at least two of them.

[0021] In some embodiments, the organic ion-particle-modified crystal material includes: Pyr 11 FSI, Pyr 12 FSI or N 1122 Any one or at least a combination of two of the FSIs.

[0022] In some embodiments, the mass ratio of the PVDF polymer matrix to the lithium salt is 1:(0.3-2.0), for example, 1:0.3, 1:0.6, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.7, 1:2 or any range between the above values, preferably 1:(0.8-1.5).

[0023] In some embodiments, the mass ratio of the PVDF polymer matrix to the organic ion-derived plastic crystal material is 1:(0.05-1.5), for example, 1:0.05, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.2, 1:1.5 or any range between the above values, preferably 1:(0.2-0.8).

[0024] In some embodiments, the PVDF polymer matrix is ​​PVDF, the lithium salt is LiFSI, and the organic ion-particle crystallizing material is Pyr. 11 FSI and / or Pyr 12 The mass ratio of PVDF, LiFSI and organic ion-modified crystal material is 1:1:0.6, and the mass percentage of residual solvent is 8-12 wt%.

[0025] In some embodiments, the PVDF polymer matrix is ​​PVDF, the lithium salt is LiFSI, and the organic ion-particle crystallizing material is N. 1122 The mass ratio of PVDF, LiFSI and organic ion-modified crystal material is 1:1:0.4, and the mass percentage of residual solvent is 8-12 wt%.

[0026] In a second aspect, the present invention provides a method for preparing a PVDF-based solid electrolyte as described in the first aspect, the method comprising:

[0027] S1. Mix PVDF polymer matrix, lithium salt, organic ion crystallizing material and solvent to obtain casting solution;

[0028] S2. After the casting solution forms a wet film, it is dried to obtain the PVDF-based solid electrolyte.

[0029] In some embodiments, the mass ratio of the PVDF polymer matrix to the solvent is 1:(2-40), for example 1:2, 1:4, 1:6, 1:8, 1:10, 1:12, 1:14, 1:15, 1:16, 1:18, 1:20, 1:22, 1:25, 1:26, 1:34, 1:40 or any range between the above values, preferably 1:(4-25).

[0030] In some embodiments, the mixing temperature is 20-80°C, for example 20°C, 30°C, 40°C, 60°C, 70°C, 80°C or any of the above values, preferably 40-70°C, and the time is 2-24 h, for example 2h, 6h, 10h, 16h, 20h, 24h or any of the above values, preferably 6-12 h.

[0031] In some embodiments, the method of forming a wet film includes, but is not limited to, casting, coating, or casting.

[0032] In some embodiments, the drying temperature is 30-100°C, such as 30°C, 40°C, 60°C, 70°C, 90°C, 100°C or any of the above values, preferably 50-70°C, and the drying time is 6-72 h, such as 6 h, 18 h, 30 h, 48 h, 60 h, 72 h or any of the above values, preferably 12-48 h.

[0033] In some embodiments, the preparation method includes:

[0034] S1. Stir the PVDF polymer matrix, lithium salt, organic ion crystallizing material and solvent at 20-80℃ for 2-24h to obtain a uniform casting solution;

[0035] S2. The casting solution is allowed to stand or be degassed under vacuum, and then cast, coated or cast, and dried under vacuum or forced air conditions at 30-100℃ for 6-72 h to obtain the PVDF-based solid electrolyte.

[0036] Thirdly, the present invention provides a lithium metal battery, including a positive electrode, a negative electrode, and a PVDF-based solid electrolyte as described in the first aspect, disposed between the positive electrode and the negative electrode.

[0037] In some embodiments, the film thickness of the PVDF-based solid electrolyte is 10-300 μm, such as 10 μm, 50 μm, 100 μm, 150 μm, 200 μm, 300 μm or any of the above values, preferably 80-150 μm.

[0038] In some embodiments, the positive electrode sheet includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material includes any one or a combination of at least two of LiFePO4, LiCoO2, NCM811, NCM622, NCM523, or NCA, preferably NCM811. The conductive agent includes any one or a combination of at least two of Super P, acetylene black, carbon nanotubes, and graphene, preferably Super P. The binder includes one or more of PVDF, PVDF-HFP, and P(VDF-TrFE), preferably PVDF.

[0039] In some embodiments, the positive electrode is an NCM811 positive electrode, composed of NCM811, Super P, and PVDF in a mass ratio of 8:1:1, and the areal loading of the positive electrode active material is 1.0-2.5 mg / cm³. 2For example, 1 mg / cm 2 1.2 mg / cm 2 1.5 mg / cm 2 1.8 mg / cm 2 2 mg / cm 2 2.2 mg / cm 2 2.5 mg / cm 2 Or a range between any of the above values.

[0040] In some embodiments, the negative electrode is a lithium metal negative electrode or a composite negative electrode. The lithium metal negative electrode includes lithium sheets, lithium foils, etc. The composite negative electrode includes a negative electrode current collector and a lithium-containing active material layer disposed on the surface of the negative electrode current collector.

[0041] In some embodiments, the composite solid electrolyte membrane may be a cast membrane, a coated membrane, a blade-coated membrane, a cast film, a hot-pressed membrane, or a composite membrane loaded on a porous support, preferably a PVDF-based cast membrane.

[0042] In some embodiments, the lithium metal battery may be a button cell, a pouch cell, a stacked cell, a wound cell, a cylindrical cell, or a prismatic cell, preferably a button cell or a pouch cell.

[0043] In some embodiments, the lithium metal battery is an NCM811||Li coin cell, comprising an NCM811 positive electrode, a film layer formed by the solid electrolyte described in the first aspect, and a lithium metal negative electrode.

[0044] The present invention also provides a method for preparing the lithium metal battery, comprising: preparing a positive electrode sheet; preparing a composite solid electrolyte membrane; stacking the positive electrode sheet, the composite solid electrolyte membrane and the lithium metal negative electrode in sequence; and assembling them into a coin cell, a pouch cell, a stacked cell, a cylindrical cell or a square cell under an inert atmosphere.

[0045] In some embodiments, the solid electrolyte membrane described in this invention can also be introduced into the positive electrode as an ion-conducting component to improve the ion transport capability inside the positive electrode.

[0046] In some embodiments, the lithium metal battery using the solid electrolyte membrane of the present invention exhibits excellent performance, wherein the NCM811||Li button cell achieves a cutoff voltage of 4.3 V and a loading of 1.5 mg / cm³. 2 The cycle life at 5C is no less than 500 cycles, and the discharge specific capacity is no less than 120 mAh·g. -1 After 500 cycles, the capacity retention is no less than 80%, and the coulombic efficiency is no less than 99%; it can achieve stable cycling at -10℃ and 0.1 C, and the discharge specific capacity is no less than 150 mAh·g after 100 cycles. -1.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] (1) The PVDF-based solid electrolyte provided by the present invention can be applied to lithium metal batteries to improve lithium ion migration ability, reduce ion migration energy barrier, and improve battery capacity retention and cycle stability.

[0049] (2) The lithium metal battery using the solid electrolyte membrane described in this invention has excellent performance, among which the most excellent performance is that the NCM811||Li button cell has a cutoff voltage of 4.3 V and a loading of 1.5 mg / cm³. 2 Under 5C, room temperature testing conditions, the cycle life is no less than 750 cycles, the capacity retention is no less than 80%, the coulombic efficiency is no less than 98%, and the initial discharge specific capacity is no less than 120 mAh·g. -1 Furthermore, it can achieve 180 stable cycles at -10℃ and 0.1C, with an initial discharge specific capacity of not less than 150 mAh·g. -1 The capacity retention rate is approximately 100%. Attached Figure Description

[0050] Figure 1 The prepared Pyr 12 FSI 1H NMR spectrum;

[0051] Figure 2 The prepared Pyr 11 FSI 1H NMR spectrum;

[0052] Figure 3 To prepare N 1122 FSI 1H NMR spectrum;

[0053] Figure 4 Comparison of surface and cross-sectional SEM images of solid electrolytes PL, P11@PL, P12@PL, and N1122@PL, respectively;

[0054] Figure 5 The images show a comparison of the SEM morphology of the lithium metal surface after 50 cycles of lithium-lithium symmetric batteries assembled using PL, P11@PL, P12@PL, and N1122@PL solid electrolytes.

[0055] Figure 6 The figures show the performance of lithium-lithium symmetric batteries assembled using solid electrolytes PL, P11@PL, P12@PL, and N1122@PL, respectively.

[0056] Figure 7The figures show the 5C performance test results of NCM811||Li batteries assembled using solid electrolytes PL, P11@PL, P12@PL, and N1122@PL. Detailed Implementation

[0057] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0058] Unless otherwise specified, the raw materials involved in the following specific embodiments of the present invention are all conventional materials in the art, and can be purchased from commercially available products. Some raw material information is as follows:

[0059] PVDF: Purchased from Krohde, brand name ARKEMA, product number MA-EN-BI-002302, molecular weight 6.0×10⁻⁶ 5 g / mol.

[0060] Example 1

[0061] This embodiment provides a Pyr 12 The preparation method of FSI organic ion-plastinated crystal material, with the following reaction formula:

[0062] ;

[0063] The preparation method is as follows:

[0064] 1-Methylpyrrolidine and 1-bromoethane were uniformly dispersed in an appropriate amount of tetrahydrofuran at a molar ratio of 1:1. The mixture was stirred at 60 °C for 12 h. The product was washed three times with diethyl ether and then dried under vacuum at 80 °C for 6 h to obtain a white solid product 1. The aqueous solution containing product 1 was slowly added to a LiFSI aqueous solution (the molar ratio of product to LiFSI was 1:1.1). The mixture was stirred at room temperature for 12 h. After filtering the solution, the white solid was collected, washed three times with deionized water, and then dried under vacuum at 100 °C for 12 h to obtain a white solid product Pyr. 12 FSI.

[0065] Example 2

[0066] This embodiment provides a Pyr 11 The preparation method of FSI organic ion-plastinated crystal material, with the following reaction formula:

[0067] ;

[0068] The preparation method is as follows:

[0069] 1-Methylpyrrolidine and iodomethane in a molar ratio of 1:1 were uniformly dispersed in an appropriate amount of tetrahydrofuran. The mixture was stirred at 0°C for 12 h. The product was washed three times with diethyl ether and then dried under vacuum at 80°C for 6 h to obtain a white solid product 1. The aqueous solution containing product 1 was slowly added to an aqueous LiFSI solution (the molar ratio of product to LiFSI was 1:1.1). The mixture was stirred at room temperature for 12 h. After filtering the solution, the white solid was collected, washed three times with deionized water, and then dried under vacuum at 100°C for 12 h to obtain a white solid product Pyr. 11 FSI.

[0070] Example 3

[0071] This embodiment provides an N 1122 The preparation method of FSI organic ion-plastinated crystal material, with the following reaction formula:

[0072]

[0073] The preparation method is as follows:

[0074] Dimethylethylamine and bromoethane in a molar ratio of 1:1 were uniformly dispersed in an appropriate amount of tetrahydrofuran. The mixture was stirred at 40 °C for 12 h. The product was washed three times with diethyl ether and then dried under vacuum at 80 °C for 6 h to obtain a white solid product 1. The aqueous solution containing product 1 was slowly added to a LiFSI aqueous solution (the molar ratio of product to LiFSI was 1:1.1). The mixture was stirred at room temperature for 12 h. After filtering the solution, the white solid was collected, washed three times with deionized water, and then dried under vacuum at 100 °C for 12 h to obtain a white solid product N. 1122 FSI.

[0075] Figure 1-3 The prepared Pyr 12 FSI, Pyr 11 FSI, N 1122 The FSI nuclear magnetic resonance hydrogen spectrum shows that the present invention has successfully prepared three organic ion-based plastic crystal materials.

[0076] Example 4

[0077] This embodiment provides a PVDF-based solid electrolyte and its preparation method, as follows:

[0078] According to PVDF:LiFSI:Pyr 12 The FSI:DMF mass ratio was 1:1:0.6:16. The above substances were weighed into a glass bottle and stirred at 60°C for 12 h. After the resulting solution was allowed to stand for 6 h to defoam, it was cast into a mold and dried under vacuum at 60°C for 40 h. The residual DMF solvent content was about 9 wt%. The electrolyte membrane was named P12@PL.

[0079] Example 5

[0080] This embodiment provides a PVDF-based solid electrolyte and its preparation method, as follows:

[0081] According to PVDF:LiFSI:Pyr 11 The FSI:DMF mass ratio was 1:1:0.6:16. The above substances were weighed into a glass bottle and stirred at 60°C for 12 h. After the resulting solution was allowed to stand for 6 h to defoam, it was cast into a mold and dried under vacuum at 60°C for 40 h. The residual DMF solvent content was about 9 wt%. The electrolyte membrane was named P11@PL.

[0082] Example 6

[0083] This embodiment provides a PVDF-based solid electrolyte and its preparation method, as follows:

[0084] According to PVDF:LiFSI:N 1122 The FSI:DMF mass ratio was 1:1:0.4:16. The above substances were weighed into a glass bottle and stirred at 60°C for 12 h. After the resulting solution was allowed to stand for 6 h to defoam, it was cast into a mold and dried under vacuum at 60°C for 40 h. The residual DMF solvent content was about 9 wt%. The electrolyte membrane was named N1122@PL.

[0085] Example 7

[0086] This embodiment provides a PVDF-based solid electrolyte and its preparation method.

[0087] The difference from Example 4 is that in this example, only Pyr is changed. 12 The amount of FSI added was used to prepare different Pyr 12 FSI-added composite solid electrolyte membrane, PVDF:Pyr 12 The mass ratios of FSI were 1:0.2 (Example 7-1), 1:0.4 (Example 7-2), and 1:0.8 (Example 7-3).

[0088] Example 8

[0089] This embodiment provides a PVDF-based solid electrolyte and its preparation method.

[0090] The difference from Example 5 is that in this example, only Pyr is changed. 11 The amount of FSI added was used to prepare different Pyr 11 FSI-added composite solid electrolyte membrane, PVDF:Pyr 11The mass ratios of FSI were 1:0.2 (Example 8-1), 1:0.4 (Example 8-2), and 1:0.8 (Example 8-3).

[0091] Example 9

[0092] This embodiment provides a PVDF-based solid electrolyte and its preparation method.

[0093] The difference from Example 6 is that in this example, only N is changed. 1122 The amount of FSI added affects the preparation of different N... 1122 FSI-added composite solid electrolyte membrane, PVDF:N 1122 The mass ratio of FSI is 1:0.2 (Example 9-1) and 1:0.6 (Example 9-2).

[0094] Example 10

[0095] This embodiment provides a PVDF-based solid electrolyte and its preparation method.

[0096] The difference from Example 5 (P11@PL) is that, in this example, by controlling the drying time, the residual solvent content in the obtained PVDF-based solid electrolyte is 5 wt% (Example 10-1), 12 wt% (Example 10-2), 20 wt% (Example 10-3), and 25 wt% (Example 10-4), respectively.

[0097] Example 11

[0098] This embodiment provides a PVDF-based solid electrolyte and its preparation method.

[0099] The difference from Example 6 (N1122@PL) is that, in this example, by controlling the drying time, the residual solvent content in the obtained PVDF-based solid electrolyte is 5 wt% (Example 11-1), 12 wt% (Example 11-2), 20 wt% (Example 11-3), and 25 wt% (Example 11-4), respectively.

[0100] Comparative Example 1

[0101] This comparative example provides a blank PVDF-based solid electrolyte membrane, as follows:

[0102] According to the mass ratio of PVDF:LiFSI:DMF of 1:1:16, the above substances were weighed into a glass bottle and stirred at 60°C for 12 hours. After the resulting solution was allowed to stand for 6 hours to remove bubbles, it was cast into a mold and dried under vacuum at 60°C for 30 hours. The residual DMF solvent content was about 9 wt%. The electrolyte membrane obtained was named PL.

[0103] Performance Test 1

[0104] The microstructure of the samples provided in Examples 4, 5, 6 and Comparative Example 1 was characterized, and the results are as follows:

[0105] Figure 4 SEM images of the surface and cross-section of PL, P11@PL, P12@PL, and N1122@PL are provided to illustrate the microstructure of the electrolyte. The PL sample provided in Comparative Example 1 exhibits a morphology of numerous micrometer-diameter spherulites with a loose and porous cross-section. In contrast, the samples provided in Examples 4, 5, and 6 show significantly reduced spherulite size and a more compact cross-section. These SEM results demonstrate that the addition of organic ion-modified materials can improve the density of the electrolyte membrane and reduce the spherulite size.

[0106] Performance Test 2

[0107] The impedance and ionic conductivity of the samples provided in Examples 4-11 were tested using the following methods:

[0108] (1) Impedance: Electrochemical impedance spectroscopy (EIS) was used to measure the impedance in the frequency range of 7 MHz to 0.1 Hz with 10 mV AC oscillation. Before EIS measurement, the battery was kept at each test temperature for 1 hour to reach thermal equilibrium.

[0109] (2) Ionic conductivity: Calculated according to formula (S1):

[0110]

[0111] Where L is the electrolyte thickness, R is obtained by EIS measurement with the electrolyte sandwiched between two stainless steel gaskets, and S is the area of ​​the stainless steel gaskets.

[0112] (3) Oxidation resistance potential: determined by linear sweep voltammetry (LSV) at a scan rate of 1 mV·s -1 The test was conducted under a scanning range of OCV to 6V, with stainless steel and lithium serving as the positive and negative electrodes, respectively.

[0113] The test results are as follows:

[0114] Table 1

[0115]

[0116] As shown in Table 1, the amount of organic ion-particle-modified crystals added has a significant impact on the electrolyte impedance and ionic conductivity. Among them, the P11@PL solid electrolyte provided in Example 5 has the highest ionic conductivity.

[0117] Table 2

[0118]

[0119] As shown in Table 2, for the solid electrolyte modified with plastic crystals, the electrolyte impedance gradually decreases, the ionic conductivity gradually increases, but the oxidation resistance potential gradually decreases as the proportion of residual solvent increases. Combining the test results of the three types in Table 2, it can be seen that when the proportion of residual solvent is between 8-12%, the electrolyte has lower impedance and better ionic conductivity and oxidation resistance potential.

[0120] Performance Test 3:

[0121] The performance of the samples provided in Examples 4-6 and Comparative Example 1 was tested using the following methods:

[0122] (1) Ionic conductivity: Same as the ionic conductivity test in performance test 2, calculated according to formula (S1).

[0123] (2) Lithium-ion transference number: Assemble a Li||Li symmetric cell and apply a polarization voltage (ΔV=10 mV).

[0124] Lithium transference number was determined with a bias time of over 4000 s; simultaneously, EIS measurements were performed using a 10mV AC oscillation within a frequency range of 7 MHz to 0.1 Hz to analyze the initial and steady-state characteristics of the battery. The following formula was used for calculation:

[0125]

[0126] Where ΔV is the polarization voltage, and I0 and I S These are the initial current and steady-state current, R0 and R... S These are the interface resistances before and after biasing.

[0127] (3) Activation energy: The activation energy is calculated according to the Arrhenius equation (S3):

[0128]

[0129] Where σ is the ionic conductivity, σ0 is the pre-exponential factor, and k B Here, E is Boltzmann's constant, T is Kelvin temperature, and E is... a It is the activation energy.

[0130] (4) Tensile strength: A universal testing machine was used to perform tensile tests on rectangular specimens with a width of 5 mm. The initial gauge length of the fixtures was set to 20 mm, and the tensile speed was set to 5 mm·min. -1 until the sample breaks.

[0131] (5) Oxidation potential: Same as the oxidation potential test in performance test 2.

[0132] (6) Temperature-dependent AC impedance spectroscopy: The test was performed using a Bio-Logic SAS SP-200 electrochemical workstation at a temperature range of 25~80℃ and a frequency range of 7 MHz to 0.1 Hz, with stainless steel (SS) as the blocking electrode.

[0133] (7) Long-cycle test of Li||Li symmetric battery: Li||Li symmetric battery was assembled using CR2032 button cell casing, with a lithium sheet area of ​​1.96 cm². 2 The assembly sequence is as follows: positive electrode shell, stainless steel gasket, lithium sheet, electrolyte membrane, lithium sheet, stainless steel gasket, spring contact, and negative electrode shell. The test conditions are: first, a current density of 0.05 mA·cm². -2 The surface area capacity is 0.05 mAh·cm³. -2 Activation was performed at a current density of 0.1 mA·cm⁻¹. -2 The surface area capacity is 0.1 mAh·cm³. -2 A constant current long-cycle test was then performed.

[0134] (8) Performance testing of lithium metal button cells: LiNi batteries were assembled using CR2025 type button cells. 0.8 Co 0.1 Mn 0.1 The O2(NCM811)||Li full cell is assembled in the following order: positive electrode shell, NCM811 positive electrode sheet, electrolyte membrane, lithium metal negative electrode sheet, stainless steel gasket, spring contact, and negative electrode shell. The areal loading of the positive electrode active material is 1.0-2.0 mg·cm³. -2 The test voltage range is 3.0-4.3 V. The battery is first activated at a 0.1 C rate, and then subjected to a constant current charge-discharge long cycle test at a 5 C rate.

[0135] (9) Low-temperature performance test of lithium metal button battery: The assembly conditions are the same as (8). The battery test voltage range is 3.0-4.3V. The battery is first activated at 0.1C at room temperature of 25℃, and then transferred to -10℃ and left for more than 8 hours before 0.1C and 0.2C long cycle tests are performed.

[0136] The test results are as follows:

[0137] Figure 5 The SEM images of the lithium metal surface after 50 cycles using the solid electrolytes provided in Examples 4, 5, 6 and Comparative Example 1 are shown. The results show that the solid electrolyte provided by the present invention can promote uniform deposition of lithium metal, thereby suppressing the formation of lithium metal side dendrites, and demonstrating its potential to be adapted to lithium metal battery systems.

[0138] Figure 6To demonstrate the long-cycle performance of the lithium-lithium symmetric battery, Example 5 exhibits the lowest cycle overpotential and a longer stable cycle time, as shown in Table 3.

[0139] Figure 7 The table shows the long-cycle performance of the NCM811||Li battery at a 5 C charge / discharge rate. Example 5 exhibits the highest initial discharge specific capacity and the longest stable cycle count. Specific data are shown in Table 3.

[0140] Performance data are shown in Table 3:

[0141] Table 3

[0142]

[0143] As shown in Table 3, the solid electrolyte provided by the present invention has higher ionic conductivity and lithium-ion transference number, while its mechanical properties are improved, its tensile strength is excellent, its oxidation potential is improved, and it can be matched with high-voltage cathodes such as NCM811, while reducing the ion migration energy barrier.

[0144] When applied to batteries, it exhibits superior cycle stability, initial discharge specific capacity, capacity retention, and average coulombic efficiency, as well as excellent low-temperature performance.

[0145] The present invention has been illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A PVDF-based solid electrolyte, characterized in that, It includes PVDF polymer matrix, lithium salt, organic ion-modified crystal material and residual solvent.

2. The PVDF-based solid electrolyte according to claim 1, characterized in that, The residual solvent includes any one or a combination of at least two of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone or dimethyl sulfoxide, preferably N,N-dimethylformamide; And / or, based on the total mass of the PVDF-based solid electrolyte as 100%, the mass percentage of the residual solvent is 5-25 wt%, preferably 5-20 wt%, and more preferably 8-12 wt%.

3. The PVDF-based solid electrolyte according to claim 1 or 2, characterized in that, The lithium salt includes any one or a combination of at least two of LiFSI, LiTFSI, LiDFOB, LiBOB, LiBF4, LiPF6, LiClO4 or LiNO3, with LiFSI being preferred.

4. The PVDF-based solid electrolyte according to any one of claims 1-3, characterized in that, The cationic structure of the organic ion-plastinated crystal material includes any one or a combination of at least two of the following: 1-ethyl-1-methylpyrrolidineonium ion, 1,1-dimethylpyrrolidineonium ion, or dimethyldiethylammonium ion; and the anion includes FSI. - TFSI - DFOB - BOB - BF4 - or PF6 - Any one or at least two of them; Preferably, the organic ion-plastining material includes: Pyr 11 FSI, Pyr 12 FSI or N 1122 Any one or at least a combination of two of the FSIs.

5. The PVDF-based solid electrolyte according to any one of claims 1-4, characterized in that, The mass ratio of the PVDF polymer matrix to the lithium salt is 1:(0.3-2.0), preferably 1:(0.8-1.5).

6. The PVDF-based solid electrolyte according to any one of claims 1-5, characterized in that, The mass ratio of the PVDF polymer matrix to the organic ion-derived plastic crystal material is 1:(0.05-1.5), preferably 1:(0.2-0.8).

7. The PVDF-based solid electrolyte according to any one of claims 1-6, characterized in that, The PVDF polymer matrix includes any one or a combination of at least two of PVDF, PVDF-HFP, P(VDF-TrFE), P(VDF-TrFE-CTFE), or blends or derivatives of PVDF with the above copolymers.

8. A method for preparing a PVDF-based solid electrolyte as described in any one of claims 1-7, characterized in that, The preparation method includes: S1. Mix PVDF polymer matrix, lithium salt, organic ion crystallizing material and solvent to obtain casting solution; S2. After the casting solution forms a wet film, it is dried to obtain the PVDF-based solid electrolyte.

9. The preparation method according to claim 8, characterized in that, The mass ratio of the PVDF polymer matrix to the solvent is 1:(2-40), preferably 1:(4-25).

10. A lithium metal battery, characterized in that, It includes a positive electrode, a negative electrode, and a PVDF-based solid electrolyte as described in any one of claims 1-7 disposed between the positive electrode and the negative electrode; Preferably, the film thickness of the PVDF-based solid electrolyte is 10-300 μm, and more preferably 80-150 μm.

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